So this is the kind of writings you garner your insights from? This particular scripture is flawed.
Let me take the example of the passive radiator they describe, and which they call a 5th order filter. It ain't. The passive radiator is a spring-mass loaded resonator, very much like the air mass in a vent, working against the air spring of the enclosure. Both vented and passive radiator are effectively 4th order high pass filters. Yes, the passive radiator has its own resonant frequency. However, this frequency is typically chosen such that it falls outside the pass band. There is no difference with a vent, which also has its own resonance frequency (albeit much higher, usually placed on the other side outside the pass band, but you need an electric low pass for that).
You can easily verify this from the group delay graph they show of a passive radiator enclosure. In the pass band, it behaves like a 4th order filter. Only at the extreme low end, there is a rapid phase shift, but this is where the driver and the radiator have long stopped producing useful sound.
I am not arguing that it is not a nice experiment to see what happens if we convolve a signal with an all pass filter with inverse phase shift, or any other means you might think of, to linearize phase. It has been done and the results are mixed. But please use the right metric, because if you look at group delay, you overemphasize the low end, without any psyco-acoustic or other reasons to do so.
A misguided focuss on group delay often leads to wrong conclusions, for example that a bass reflex enclosure is worse than a sealed one, because it exhibits more group delay. Why is JBL's latest flag ship housed in a BR enclosure? It is not because the Harman engineers are unaware of theory. I'd explain why, but you don't answer to arguments anyways, so why even bother.
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For you math wizzes here is a GD question. If you use a sealed enclosure, which I see is a 2nd order system with least phase shift, what happens when you electronically eq the low frequency and lower the .3db point electronically? Does the EQ now increase the group delay the same as a vented 4th order system or does it still follow the smooth phase slope of the 2nd order acoustical system? Yes I know it will take more amplifier power at the lower limit but that being not an issue what happens to the phase response and by derivation the GD? Will it become equivalent to the vented system?
Kindhornman, if you electronically eq the - 3dB point down, you move the place where phase shift occurs to a lower point as well.
The phase shift depends on the slope chosen to fall off at the low end. Just remember that frequency response and phase shift are two sides of the same medal. For every 6dB of slope per octave, you introduce 90 degrees of phase shift, distributed equally around the - 3dB point. It does not matter if the change in frequency response happens because of electric or physical processes. It is all minimum phase.
In other words, it all depends on what kind of filter you put in on the low end. You need one, because if you would eq the - 3dB point down to dc, your cones would fly through the room. It is a decision to make it 6, 12 or whatever dB/octave, so you can influence the phase shift that way (but low filter orders will require extraordinary amounts of power and excursion capability).
The phase shift depends on the slope chosen to fall off at the low end. Just remember that frequency response and phase shift are two sides of the same medal. For every 6dB of slope per octave, you introduce 90 degrees of phase shift, distributed equally around the - 3dB point. It does not matter if the change in frequency response happens because of electric or physical processes. It is all minimum phase.
In other words, it all depends on what kind of filter you put in on the low end. You need one, because if you would eq the - 3dB point down to dc, your cones would fly through the room. It is a decision to make it 6, 12 or whatever dB/octave, so you can influence the phase shift that way (but low filter orders will require extraordinary amounts of power and excursion capability).
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Thanks Vacuphile, that is clear and I understand what you are saying. So if you eq the -3 db point to match the reflex tuning and used a higher order hi-pass filter of 4th order you would have the 360 phase shift placed around the -3db point which I think would be the same as a reflex loading of equivalent tuning.
We still have no data from controlled experiments to tell us that audible problems at low frequencies are linked to GD numbers in an “effect-cause” relation.
It is many years now that the assumed equation ‘high GD= bad bass’ is repeated unproven in books, magazines and internet talk that it is hard to question it’s validity without raising a lot of reaction.
I am with vacuphile that the effects of a reverb space on the phase at LF, are a good indication for showing that GD is not a meaningful number for our perception of LF sound.
I would like to read Tom Danley’s opinion on this, as he has been involved in producing a lot of LFs and some good amounts of VLFs for some decades. He should have noticed something by now!
George
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For those who want to talk about subjective qualities, I have an observation.
In 2L-086 here (use the browser search function):
High Resolution Music DOWNLOAD services .:. FLAC in free TEST BENCH
At the beginning there is a loud horn, quieter bells, and then a quieter horn. The same distortion which causes the quieter horn to be hard to single out, also causes painfully harsh sound in my perception. I think that when something causes difficulty in separating different sounds, our hearing system seems to default to perceiving it as a hearing obstruction, which can register as ear pain or as feeling sensations in the ear area. On the other hand, when everything is heard clearly, you want to turn the volume up even if it isn't actually quieter.
At any rate, what kind of distortion best fits this description?
In 2L-086 here (use the browser search function):
High Resolution Music DOWNLOAD services .:. FLAC in free TEST BENCH
At the beginning there is a loud horn, quieter bells, and then a quieter horn. The same distortion which causes the quieter horn to be hard to single out, also causes painfully harsh sound in my perception. I think that when something causes difficulty in separating different sounds, our hearing system seems to default to perceiving it as a hearing obstruction, which can register as ear pain or as feeling sensations in the ear area. On the other hand, when everything is heard clearly, you want to turn the volume up even if it isn't actually quieter.
At any rate, what kind of distortion best fits this description?
George, I have read a study once, believe it was done by some Scandinavians, comparing preferences for either closed or vented enclosures, based on listening tests. The audiophiles, if I remember correctly, had a preference for closed, all the rest of mankind for vented. Does this ring a bell with you? Anyhow, it still doesn't prove anything in particular about the audibility of GD.
Like you, I'd be very much interested in learning Tom Danley's take on this.
Like you, I'd be very much interested in learning Tom Danley's take on this.
Sy made a comment about a year ago about how there are sentences we can make that are grammatically correct but make no sense when it comes to physics. I think the thread had to do with the expanding universe.
I think, in my own limited way that our comprehension is completely outclassed by the complexity of our existence and that we are completely ill-equipped at this stage to expect our understanding of these matters to continue to progress at the rate of discovery we have had over the past 500 years.
Physics isn't soft or hard, it's our own experience that lacks the kind of pliability required to ignore the use of our own cultural and historical shackles that confine our ability to explore space as it behaves.
What is really hard, is to accept that we build from small ideas to big ones. But its form is not like a ladder where we can just reach over, it is a broad step staircase: If the stair-step is faulty, we may or may not be able to get back to the previous before we fall to the bottom depending on the risks involved.
Boolean math was around for a long time before computers came to be. At the time it had use, but just like many types of math that most people would consider "pie in the sky" who knows how we will try to use a model when it is first established.
So... in the end - as you say, Physics in all it's dynamics may be soft. It is the state of humans that it is so hard to work with. If we allow ourselves to use phrases that are of the same utility as "Good enough for gubam!nt work" then I worry about the utility of those steps, to a much greater degree than I do about demonstrably reliable prior art.
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It seems that physics had changed a lot our perception of the Universe. During all the previous centuries, it was a science that increased our understanding. Recently (Bozon de Higgs, dark matter, dark energy etc.) it just increases the evaluation of our unknowing. 96% of the universe seems a pure mystery.
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This is an easy one.
The rest of mankind was wrong.
George
A common thread between the two is that GD is lower for the closed box, also.
Coincidence? No.
If it doesn't really matter, then make a infrasonic HP filter anyway you want for the TT/LP junk and you wont hear any difference in music bass timbre/quality...... Just a cleaner (lower distortion) sound... right?
-RNM
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Okay, downloaded and had a listen. No problems here, but what the recording has, to my ears, is an over reverberant acoustic - why did they do that?? An instrument with a very strong attack, which is recorded in a highly echoing space is about as severe a test of a system's resolution as it gets - if the replay has any problems then it will register as distortion.
You're right about the difficulty of sound separation being key; this is why a lot of ambitious pop productions are troublesome on many systems - when the system is raised to a sufficient quality level, and everything is heard clearly, then the volume can be turned up to any level one wishes - the individual sound elements within still retain their individual character, and the ear has no problems registering it all; in fact, it delights in the complexity, the interwoven structure of the total ...
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Lumpy bass is defective bass as far as I'm concerned, you never hear this from live instruments - if I'm aware of some bass notes thundering away all the time then it's just a crap system, end of story - the worst offender I heard recently was https://steinwaylyngdorf.com/products/model-d-speaker, absolutely appalling sound ...
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Well, I lied to you a bit with that.
It is a 15Hz 48dB/oct (LR) LP filter that I use.
I really can’t ‘hear’ it.
But my set-up suffers from a lot of curses (digitalitis, DSPitis, Dampitis, OBitis, Uframitis, Wframitis)
George
George, I have not started looking at it yet but how well does miniDSP handle the large difference in low frequency IIR coefficients?
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